Size reduction of metal-oxide-semiconductor field-effect transistors (MOSFETs) and FinFETs, including reduction of the gate length and gate oxide thickness, has enabled the continued improvement in speed, performance, density, and cost per unit function of integrated circuits over the past few decades. To further enhance transistor performance, MOSFET devices have been fabricated using strained channel regions located in portions of a semiconductor substrate. Strained channel regions allow enhanced carrier mobility to be realized, thereby resulting in increased performance when used for n-channel (NMOSFET) or for p-channel (PMOSFET) devices. Generally, it is desirable to induce a tensile strain in the n-channel of an NMOSFET transistor in the source-to-drain direction to increase electron mobility and to induce a compressive strain in the p-channel of a PMOSFET transistor in the source-to-drain direction to increase hole mobility. There are several existing approaches of introducing strain in the transistor channel region.
In one approach, strain in the channel region is introduced by creating a recess in the substrate in the source/drain regions. For example, a PMOS device having a compressive stress in the channel region may be formed on a silicon substrate by epitaxially growing a stress-inducing layer having a larger lattice structure than the silicon, such as a layer of SiGe, within recessed regions in the source/drain regions. Similarly, an NMOS device having a tensile stress in the channel region may be formed on a silicon substrate by epitaxially growing a stress-inducing layer having a smaller lattice structure than the silicon, such as a layer of SiP, within recessed regions in the source/drain regions.
Contact resistance may also be reduced. In one approach, a metal layer is formed over the source and drain regions. An anneal process is performed to cause a metal silicide to be formed, and un-reacted materials from the metal layer is removed. The silicide layer allows a lower contact resistance between subsequently formed contacts and the source and drain regions.